AUTOMOBILE ELECTRICAL SYSTEMS 4. HANDLING AND CARE OF BATTERY
Any battery provided in a car requires proper handling and regular care. This also involves certain safety precautions to be observed during handling and check-ups. Periodic checks ensure that battery lives its full-expected life of about 30 to 36 months. A properly maintained and fully charged battery also ensures efficient start up of the engine and functioning of other electrical systems.
4.0
Objectives After going through this lesson, you will be able to: Understand what precautions are to be taken while handling or replacing the battery in the car. Learn to take care of the battery. Know the methods of charging a battery
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4.1
Introduction
In this lesson we will study about how to handle a battery and take care of the battery fitted in the car so that it gives good service during its expected lifetime. We will also study the various methods of charging a lead-acid battery.
4.2
Handling of Battery The following safety precautions should be observed while handling a battery:
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Do not carry a flame or spark near a battery since hydrogen gas emitted out by the battery is highly combustible and may ignite, causing an explosion. Do not let the electrolyte of the battery fall on skin, clothing or the surface of the body of the car. The electrolyte is highly corrosive and any spillage should be washed away quickly with plenty of running water. Always disconnect the negative cable first and then the positive cable before removing or replacing the battery. This prevents short-circuiting of the battery through the body of the car. Tighten the battery clamps properly after the battery is installed.
Self-check Questions 1. Why a flame or spark near battery can cause explosion? 2. In case the electrolyte is spilled what should be done and why? 3. Which cable of the battery should be disconnected first and why?
4.3
Care of Battery
The expected life of an automobile battery is around three years and its reliability is also very high, but it needs proper and periodical care and maintenance at all times. • •
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Always keep the battery container clean and dry and prevent corrosion of the battery terminals by coating the terminals with petroleum jelly or shop grease. Maintain the level of the electrolyte uniformly up to the upper level mark in the container in all cells. In opaque containers, it should be ensured that the level of the electrolyte is at least 10 mm above the plates. When the level of the electrolyte goes down, it should be topped up with de-mineralized water or distilled water or with commercially available battery water. Tap water or ground water should never be used for topping up. Also, the plates of the battery should never be allowed to be exposed to atmosphere. Keep the battery fully charged at all times. The battery should not be left in a low state of charge for long periods of time, as this impairs the ability of the battery to get recharged. Do not let the battery to get overcharged. Overcharging a battery not only wastes electric current but also causes damage to the battery.
Self-check Questions 4. 5. 6. 7.
The expected life of an automobile battery is around __________ How can battery terminals be prevented from corrosion? Level of the electrolyte should be at least _____ above the plates Battery electrolyte should be topped up with _________________ ______________ or with ______________________________
4.4
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Battery Charging
4.4.1 Preparing a Battery for Charging •
Wash all dirt from a battery and clean its terminals before placing it on charge, but do allow dirt to get into the cells.
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Bring the electrolyte level in the cells to the correct level. If the battery is very cold, let it warm up before adding water as the level will rise as it warms up. Use only direct current from a charging source which can be controlled so that the rate of charge to the battery will not be excessive.
4.4.2 Types of Charging •
Constant current charging – This method is used when the internal condition of the cells is not known and a diagnosis of trouble is being made.
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Constant potential charging – these chargers start the charging process at a high rate and as the battery voltage builds up, the charging rate tapers off to a lower value depending on the design of the charger, and on the condition, age, and temperature of the battery.
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High rate charging – A battery may be charged at any rate which does not cause the electrolyte temperature of any cell to exceed 53OC and does not cause excessive loss of electrolyte. High rate chargers are usually constant potential machines of very high capacity so that initial charge rates of 40 to 50 amp are common. High rate charger may be used to sufficiently charge the battery so that it continues to give service depending on its condition and state of charge.
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Trickle charging - These are mainly used to keep display batteries charged and ready for sale.
4.4.3 Constant Current Charging Method • •
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Connect the positive lead of the charger to the positive terminal of the battery and the negative lead of the charger to the negative terminal of the battery. If several batteries are being charged in series, they should be connected from the positive terminal of one to the negative terminal of the other so that finally we have a positive and negative terminal free for connecting to the charger. A safe rate of bench charging is 1 amp/positive plate/cell. If several batteries of different sizes are being charged in series the rate for the line must be determined by the smallest battery in the circuit. If necessary, the batteries may be left on charge overnight at one-half the daytime rate of charge. If the temperature of any battery reaches 43OC, lower the charging rate. Hydrometer readings should be recorded hourly for each cell of each battery as soon as it approaches the fully charged state. A battery is considered fully charged when the cells are all gassing freely and specific gravity ceases to rise for 3 consecutive readings taken at hourly intervals. Most batteries can be charged at normal rates in 12 to 16 hours. A badly sulphated battery will require longer than a normal battery.
Self-check Questions 8. ______ is used for charging a battery 9. Name the different methods of battery charging. 10. _______________________ method is used when the internal condition of the cells is not known 11. ________________________ start the charging process at a high rate and as the battery voltage builds up, the charging rate tapers off to a lower value 12. A battery may be charged at any rate which does not cause the electrolyte temperature of any cell to exceed _________ 13. High rate chargers are usually _____________________ of very high capacity so that initial charge rates of ___________ are common 14. Trickle charging is mainly used to __________________________ 15. For constant current charging, a safe rate of bench charging is ____________________________ 16. In constant current charging, if the temperature of any battery reaches _________, lower the charging rate. 17. When would you consider a battery to be fully charged? 18. Most batteries can be charged at normal rates in _____________ 19. A badly sulphated battery will require ________ than a normal battery to charge.
4.5
Assignments
4.5.1 Class Assignment 1. Discuss the precautions taken during handling a battery. 2. How would take care of battery to get good life. 3. Discuss various methods of charging the battery 4.5.2 Home Assignment 1. Write a note on constant current charging
4.6
Summing Up
In this lesson we learnt about handling and taking care of the battery. We further studied the various charging methods and saw that the battery can be damaged due to both overcharging and undercharging. Also it should be remembered that a flame or spark near a battery can possibly cause an explosion. Hence necessary precautions should be observed. With this lesson we have covered the study of all systems on the chassis of a vehicle. What now remains is to practice all that we have studied.
4.7
Possible Answers to Self-check Questions
1. hydrogen gas emitted out by the battery is highly combustible and may ignite causing an explosion 2. wash quickly with plenty of running water because electrolyte is highly corrosive 3. Negative cable, then return path will not be available and short-circuiting of battery through body of car will not take place 4. three years 5. by coating the terminals with petroleum jelly or shop grease 6. 10 mm 7. de-mineralized water or distilled water or with commercially available battery water 8. direct current 9. Constant current charging, Constant potential charging, High rate charging, Trickle charging 10. Constant current charging 11. Constant potential chargers 12. 53OC 13. constant potential machines, 40 to 50 amp 14. keep display batteries charged and ready for sale 15. 1 amp/positive plate/cell 16. 43OC 17. when the cells are all gassing freely and specific gravity ceases to rise for 3 consecutive readings taken at hourly intervals 18. 12 to 16 hours 19. longer
4.8 1. 2. 3. 4.
4.9
Terminal Questions List the precautions you should take during handling a battery. How would take care of a battery to get good life. Describe the various methods of charging the battery Write a note on constant current charging
References
1. Battery Service Manual, 3rd Ed., 1961. Standard Batteries Ltd, Bombay.
4.10 Suggested Further Reading 1. Kohli, P.L., 1987. Automotive Electrical Equipment. First Reprint. Tata McGrawHill Publishing Co. Ltd, New Delhi. 2. Crouse, W. H., 1966. Automotive Electrical Equipment. McGraw-Hill Book Co., New York.
4.11 Glossary Tapering charging rate
In a constant potential machine, the charging rate tapers i.e. decreases, at the same setting of the charger when the battery comes up to charge.
Combustible
Flammable, explosive, burnable.
Hydrometer
An instrument used to measure the specific gravity (density of liquid w.r.t. water) of a liquid.
Top up
The process of maintaining the level of electrolyte in the battery by adding distilled water is known as top up.
Trickle charging
Slow rate of charging, say at 1 amp, to keep the battery in charged condition by overcoming the effects of selfdischarge.